EP1428662B1

EP1428662B1 - Monolithic ink-jet printhead and method for manufacturing the same

Info

Publication number: EP1428662B1
Application number: EP03257587A
Authority: EP
Inventors: Hoon Song; Yong-Soo Oh; Jong-Woo Shin; Chang-Seung Lee; Hung-Taek Lim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2002-12-05
Filing date: 2003-12-02
Publication date: 2008-02-27
Anticipated expiration: 2023-12-02
Also published as: KR20040049151A; JP2004181968A; US20040109043A1; DE60319328D1; EP1428662A2; EP1428662A3; DE60319328T2; US7104632B2; US20060290743A1; KR100468859B1

Description

The present invention relates to an ink-jet printhead, and more particularly, to a thermally driven monolithic ink-jet printhead in which a nozzle plate is formed integrally with a substrate and a hydrophobic coating layer is formed on a surface of the nozzle plate, and a method for manufacturing the same.
Generally, ink-jet printheads are devices for printing a predetermined color image by ejecting small droplets of printing inks at desired positions on a recording sheet. Ink-jet printheads are largely classified into two types depending on the ink droplet ejection mechanisms: a thermally driven ink-jet printhead in which a heat source is employed to form and expand bubbles in ink, thereby causing ink droplets to be ejected, and a piezoelectrically driven ink-jet printhead in which a piezoelectric crystal bends to exert pressure on ink, thereby causing ink droplets to be expelled.
An ink droplet ejection mechanism of the thermally driven ink-jet printhead will be now described in detail. When a pulse current flows through a heater consisting of a resistive heating material, heat is generated by the heater to rapidly heat ink near the heater to approximately 300°C, Accordingly, the ink boils and bubbles are formed in the ink. The formed bubbles expand and exert pressure on the ink contained within an ink chamber. This causes a droplet of ink to be ejected through a nozzle from the ink chamber.
Here, thermally driven ink-jet printing can be further subdivided into top-shooting, side-shooting, and back-shooting types depending on the direction of ink droplet ejection and the directions in which bubbles expand. While the top shooting type refers to a mechanism in which an ink droplet is ejected in the same direction that a bubble expands, the back-shooting type is a mechanism in which an ink droplet is ejected in the opposite direction that a bubble expands. In the side-shooting type, the direction of ink droplet ejection is perpendicular to the direction of bubble expansion.
Thermally driven ink-jet printheads need to meet the following conditions. First, a simple manufacturing process, low manufacturing cost, and mass production must be possible. Second, to produce high quality color images, the distance between adjacent nozzles must be as small as possible while preventing cross-talk between the adjacent nozzles. That is, to increase the number of dots per inch (DPI), many nozzles must be arranged within a small area. Third, for high speed printing, a cycle beginning with ink ejection and ending with ink refill must be as short as possible. That is, the heated ink and heater should cool down quickly so as to increase an operating frequency. Fourth, heat load exerted on the printhead due to heat generated in the heater must be small, and the printhead must operate stably under a high operating frequency.
FIG. 1A is a partial cross-sectional perspective view showing an example of a structure of a conventional thermally driven printhead disclosed in U. S. Patent No. 4,882,595 , and FIG. 1B is a cross-sectional view of the printhead of FIG. 1A for explaining a process of ejecting ink droplets.
Referring to FIGS. 1A and 1B, the conventional thermally driven ink-jet printhead includes a substrate 10, a barrier wall 14 disposed on the substrate 10 for delimiting an ink chamber 26 filled with ink 29, a heater 12 installed in the ink chamber 26, and a nozzle plate 18 having a nozzle 16 for ejecting an ink droplet 29'. If a pulse current is supplied to the heater 12, the heater 12 generates heat and a bubble 28 is formed due to the heating of the ink 29 contained within the ink chamber 26. The formed bubble 28 expands constantly to exert pressure on the ink 29 contained within the ink chamber 26, thereby causing an ink droplet 29' to be ejected through the nozzle 16 to the outside. Then, the ink 29 is introduced from a manifold 22 through an ink channel 24 to refill the ink chamber 26.
The process of manufacturing a conventional top-shooting type ink-jet printhead configured as above involves separately manufacturing the nozzle plate 18 equipped with the nozzle 16 and the substrate 10 having the ink chamber 26 and the ink channel 24 formed thereon and bonding them to each other. However, the manufacturing process is complicated and misalignment in bonding the nozzle plate 18 with the substrate 10 may be caused. Furthermore, since the ink chamber 26, the ink channel 24, and the manifold 22 are arranged on the same plane, there is a restriction on increasing the number of nozzles 16 per unit area, i.e., the density of nozzles 16. This makes it difficult to implement a high printing speed, high resolution ink-jet printhead.
Recently, to overcome the above problems of the conventional ink-jet printheads, ink-jet printheads having a variety of structures have been proposed. FIG. 2 shows an example of a monolithic ink-jet printhead laid open under publication number 20020008738 in the U. S.
Referring to FIG. 2, a hemispherical ink chamber 32 and a manifold 36 are formed on the front and rear surfaces of a silicon substrate 30, respectively, and an ink channel 34 connecting the ink chamber 32 with the manifold 36 is formed at the bottom of the ink chamber 32 to penetrate them. A nozzle plate 40 including a plurality of material layers 41, 42, and 43 stacked on the substrate 30 is formed integrally with the substrate 30.
The nozzle plate 40 has a nozzle 47 formed at a location corresponding to a central portion of the ink chamber 32, and a heater 45 connected to a conductor 46 is disposed around the nozzle 47. A nozzle guide 44 extends along the edge of the nozzle 47 toward a depth direction of the ink chamber 32. Heat generated by the heater 45 is transferred through an insulating layer 41 to ink 48 within the ink chamber 32. The ink 48 then boils to form bubbles 49. The formed bubbles 49 expand and exert pressure on the ink 48 contained within the ink chamber 32, thereby causing an ink droplet 48' to be ejected through the nozzle 47. Then, the ink 48 is introduced through the ink channel 34 from the manifold 36 due to surface tension of the ink 48 contacting the air to refill the ink chamber 32.
A conventional monolithic ink-jet printhead configured as above has an advantage in that the silicon substrate 30 is formed integrally with the nozzle plate 40 to allow a simple manufacturing process which eliminates the misalignment problem. Another advantage is that the nozzle 46, the ink chamber 32, the ink channel 34, and the manifold 36 are arranged vertically to increase the density of nozzles 46 as compared with the ink-jet printhead of FIG. 1A.
In a general ink-jet printhead, since ink is ejected in an ink droplet form, the ink must be ejected in a complete ink droplet form so as to provide a good printing performance. In the ink-jet printhead, the size, the shape, and the surface property of the nozzle affect greatly the size of the ejected ink droplet, the stability of the ink droplet ejection, and the ejection speed of the ink droplet. Particularly, the surface property of the nozzle plate affects greatly the characteristic of the ink ejection. Generally, in a case a surface of the nozzle plate has a hydrophobic property, ink can be ejected in a complete ink droplet form, thereby increasing the directionality of the ejected ink droplet and the printing quality. Further, a meniscus formed within the nozzle is more quickly stabilized after ink ejection so that air can be prevented from flowing into the ink chamber and the surface of the nozzle plate can be prevented from being polluted by ink. On the other hand, in a case the surface of the nozzle plate has the hydrophilic property, the size and the ejection speed of the ink droplet decrease.
Thus, in the monolithic ink-jet printhead shown in FIG. 2, a hydrophobic coating layer (not shown) is formed on the upper surface of the nozzle pate 40 so that the ink ejection performance is improved.
However, in the conventional monolithic ink-jet printhead shown in FIG. 2, when the hydrophobic coating layer is applied on the upper surface of the nozzle plate 40, a hydrophobic material consisting of the hydrophobic coating layer may be applied to an inner surface of the nozzle 47 and an inner surface of the ink chamber 32 other than the upper surface of the nozzle pate 40. That is, since the properties of the inner surface of the nozzle 47 and the inner surface of the ink chamber 32, which must have hydrophilic property, are changed to have hydrophobic property, it is difficult to supply the ink into the nozzle 47 and the meniscus retreats toward the ink chamber 32. As a result, the size and the ejection speed of the ink droplet decrease.
In the ink-jet printhead shown in FIG. 2, the material layers 41, 42, and 43 formed around the heater 45 are made from low heat conductive insulating materials such as oxide or nitride for electrical insulation. Thus, a considerable amount of time is required for the heater 45, the ink 48 within the ink chamber 32, and the nozzle guide 44, all of which are heated for ejection of the ink 48, to sufficiently cool down and return to an initial state, which makes it difficult to increase an operating frequency to a sufficient level.
Further, in the ink-jet printhead shown in FIG. 2, since the nozzle plate 40 is relatively thin, it is difficult to secure a sufficient length of the nozzle 47. A small length of the nozzle 47 not only decreases the directionality of the ink droplet 48' ejected but also prohibits stable high speed printing since the meniscus in the surface of the ink 48 after ejection of the ink droplet 48' moves into the ink chamber 32. To solve these problems, the conventional ink-jet printhead has the nozzle guide 44 formed along the edge of the nozzle 47. However, if the nozzle guide 44 is too long, this not only makes it difficult to form the ink chamber 32 by etching the substrate 30 but also restricts expansion of the bubbles 49. Thus, the use of the nozzle guide 44 causes a restriction on sufficiently securing the length of the nozzle 47.
According to an aspect of the present invention, there is provided a monolithic ink-jet printhead comprising: a substrate which has an ink chamber filled with ink to be ejected, a manifold for supplying ink to the ink chamber, and an ink channel for connecting the ink chamber with the manifold; a nozzle plate which includes a plurality of passivation layers sequentially stacked on the substrate, a metal layer formed on the plurality of passivation layers, and a nozzle through which ink is ejected from the ink chamber; a heater which is provided between the passivation layers and located above the ink chamber for heating ink within the ink chamber; a conductor which is provided between the passivation layers and electrically connected to the heater for applying a current to the heater; and a hydrophobic coating layer which is formed only on an outer surface of the metal layer.
It is preferable that the hydrophobic coating layer is made of a material having chemical resistance and abrasion resistance, for example, at least one of fluorine-containing compound and metal. In this case, it is preferable that the fluorine-containing compound includes polytetrafluoroethylene (PTFE) or fluorocarbon, and the metal includes gold (Au).
The metal layer is preferably made of nickel (Ni), and may be formed by electric plating to a thickness of 30-100 µm.
The nozzle may include a lower nozzle formed on the plurality of passivation layers and an upper nozzle formed on the metal layer. In this case, it is preferable that the upper nozzle has a tapered shape in which a cross-sectional area decreases gradually toward an exit.
Further, it is preferable that the nozzle plate further includes a heat conductive layer, which is located above the ink chamber, insulated from the heater and the conductor, and thermally contacts the substrate and the metal layer. In this case, the heat conductive layer may be made of any one of aluminum, aluminum alloy, gold, or silver.
According to an aspect of the present invention, there is provided a method for manufacturing a monolithic ink-jet printhead, the method comprising: (a) preparing a substrate; (b) forming a heater and a conductor connected to the heater between a plurality of passivation layers while sequentially stacking the plurality of passivation layers on the substrate; (c) forming a lower nozzle by etching the passivation layers to penetrate the passivation layers; (d) forming a metal layer on the passivation layers, forming a hydrophobic coating layer on an outer surface of the metal layer, and forming an upper nozzle connected to the lower nozzle by penetrating the metal layer and the hydrophobic coating layer; (e) etching an upper surface of the substrate exposed through the upper nozzle and the lower nozzle to form an ink chamber filed with ink; and (f) etching the substrate to form a manifold for supplying ink and an ink channel for connecting the ink chamber with the manifold.
In (a), it is preferable that the substrate is made of a silicon wafer.
In (b), it is preferable that a heat conductive layer which is located above the ink chamber, insulated from the heater and the conductor, and thermally contacts the substrate and the metal layer is formed between the passivation layers. In this case, the heat conductive layer and the conductor may be simultaneously formed from the same metal. Further, the heat conductive layer may be formed on an insulating layer after forming the insulating layer on the conductor.
In (c), the lower nozzle may be formed by dry etching the passivation layers on the inside of the heater using reactive ion etching (RIE).
It is preferable that (d) includes forming a seed layer for electric plating on the passivation layers; forming the plating mold for forming the upper nozzle on the seed layer; forming the metal layer on the seed layer by electric plating; forming the hydrophobic coating layer only on the outer surface of the metal layer; and removing the plating mold and the seed layer formed under the plating mold.
Here, the seed layer may be formed by depositing at least one of titanium and copper on the passivation layers. Meanwhile, the seed layer may include a plurality of metal layers formed by sequentially stacking titanium and copper.
The plating mold may be formed by depositing photoresist or photosensitive polymer on the seed layer to a predetermined thickness and then patterning it in the same shape as that of the upper nozzle.
At this time, it is preferable that the plating mold is formed by patterning the photoresist or the photosensitive polymer in a tapered shape, in which a cross-sectional area gradually increases downward, by a proximity exposure for exposing the photoresist or the photosensitive polymer using a photomask which is installed to be separated from a surface of the photoresist or the photosensitive polymer by a predetermined distance.
The metal layer may be made of nickel and is preferably formed to a thickness of 30-100 µm.
It is preferable that the hydrophobic coating layer is made of at least one of fluorine-containing compound and metal.
Polytetrafluoroethylene (PTFE) may be used as the fluorine-containing compound. In this case, PTFE and nickel may be compositely plated on the surface of the metal layer.
Further, fluorocarbon may be used as the fluorine-containing compound. In this case, fluorocarbon may be deposited on the surface of the metal layer using the PECVD.
Gold (Au) may be used as the metal. In this case, gold may be deposited on the surface of the metal layer using an evaporator.
In (e), the ink chamber may be formed by isotropically dry-etching the substrate exposed through the nozzle.
In (f), the manifold may be formed by etching the lower surface of the substrate, and the ink channel may be formed by etching the substrate to penetrate the substrate between the manifold and the ink chamber.
The present invention thus provides a monolithic ink-jet printhead in which a nozzle plate having a thick metal layer is formed integrally with a substrate and a hydrophobic coating layer is formed only on an outer surface of the metal layer of the nozzle plate, thereby increasing the directionality of ink ejection and the ejection performance.
The present invention also provides a method for manufacturing the monolithic ink-jet printhead.
The above advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIGS. 1A and 1B are a partial cross-sectional perspective view showing an example of a conventional thermally driven ink-jet printhead and a cross-sectional view for explaining a process of ejecting an ink droplet, respectively;
FIG. 2 is a vertical cross-sectional view showing an example of a conventional monolithic ink-jet printhead;
FIG. 3A shows a planar structure of a monolithic ink-jet printhead according to a preferred embodiment of the present invention;
FIG. 3B is a vertical cross-sectional view of the ink-jet printhead of the present invention taken along line A-A' of FIG. 3A;
FIGS. 4A through 4C illustrate an ink ejection mechanism in a monolithic ink-jet printhead according to the present invention; and
FIGS. 5 through 16 are cross-sectional views for explaining a method for manufacturing a monolithic ink-jet printhead according to a preferred embodiment of the present invention.

In the drawings the same reference numerals represent the same element, and the size of each component may be exaggerated for clarity and ease of understanding. Further, it will be understood that when a layer is referred to as being "on" another layer or a substrate, it may be located directly on the other layer or substrate, or intervening layers may also be present.
FIG. 3A shows a planar structure of a monolithic ink-jet printhead according to a preferred embodiment of the present invention, and FIG. 3B is a vertical cross-sectional view of the ink-jet printhead of the present invention taken along line A-A' of FIG. 3A. Although only a unit structure of the ink-jet printhead has been shown in the drawings, the shown unit structure is arranged in one or two rows, or in three or more rows to achieve a higher resolution in an ink-jet printhead manufactured in a chip state.
Referring to FIGS. 3A and 3B, an ink chamber 132 filled with ink to be ejected, a manifold 136 for supplying ink to the ink chamber 132, and an ink channel 134 for connecting the ink chamber 132 with the manifold 136 are formed on a substrate 110 of an ink-jet printhead.
A silicon wafer widely used to manufacture integrated circuits (ICs) may be used as the substrate 110. The ink chamber 132 may be formed in a hemispherical shape or another shape having a predetermined depth on an upper surface of the substrate 110. The manifold 136 may be formed on a lower surface of the substrate 110 to be positioned under the ink chamber 132 and is connected to an ink reservoir (not shown) for storing ink. The ink channel 134 is formed between the ink chamber 132 and the manifold 136 to perpendicularly penetrate the substrate 110. The ink channel 134 may be formed in a central portion of a bottom surface of the ink chamber 132, and a horizontal cross-sectional shape is preferably circular. However, the ink channel 134 may have various horizontal cross-sectional shapes such as oval or polygonal ones. Further, the ink channel 134 may be formed at any other location that can connect the ink chamber 132 with the manifold 136 by perpendicularly penetrating the substrate 110.
A nozzle plate 120 is formed on the substrate 110 having the ink chamber 132, the ink channel 134, and the manifold 136 formed thereon. The nozzle plate 120 forming an upper wall of the ink chamber 132 has a nozzle 138, through which ink is ejected, at a location corresponding to the center of the ink chamber 132 by perpendicularly penetrating the nozzle plate 120.
The nozzle plate 120 includes a plurality of material layers stacked on the substrate 110. The plurality of material layers includes first, second, and third passivation layers 121, 122, and 126, a metal layer 128 stacked on the third passivation layer 126 by electrical plating, and a hydrophobic coating layer 129 formed on an outer surface of the metal layer 128. A heater 142 is provided between the first and second passivation layers 121 and 122, and a conductor 144 is provided between the second and third passivation layers 122 and 126. A heat conductive layer 124 may be further provided between the second and third passivation layers 122 and 126.
The first passivation layer 121, the lowermost layer among the plurality of material layers forming the nozzle plate 120, is formed on the upper surface of the substrate 110. The first passivation layer 121 for electrical insulation between the overlying heater 142 and the underlying substrate 110 and protection of the heater 142 may be made of silicon oxide or silicon nitride.
The heater 142 overlying the first passivation layer 121 and located above the ink chamber 132 for heating ink contained in the ink chamber 132 is centered around the nozzle 138. The heater 142 consists of a resistive heating material such as polysilicon doped with impurities, tantanlum-aluminum alloy, tantalum nitride, titanium nitride, and tungsten silicide. The heater 142 may have the shape of a circular ring centered around the nozzle 138 as shown in FIG. 3A, or other shapes such as a rectangle or a hexagon.
The second passivation layer 122 for protecting the heater 142 is formed on the first passivation layer 121 and the heater 142. Similarly to the first passivation layer 121, the second passivation layer 122 may be made of silicon nitride and silicon oxide.
The conductor 144 electrically connected to the heater 142 for applying a pulse current to the heater 142 is disposed on the second passivation layer 122. One end of the conductor 144 is connected to the heater 142 through a first contact hole C₁ formed in the second passivation layer 122. The conductor 144 may be made of a highly conductive metal such as aluminum, aluminum alloy, gold, or silver.
The heat conductive layer 124 may be provided above the second passivation layer 122. The heat conductive layer 124 functions to conduct heat residing in or around the heater 142 to the substrate 110 and the metal layer 128 which will be described later, and is preferably formed as widely as possible to entirely cover the ink chamber 132 and the heater 142. The heat conductive layer 124 needs to be separated from the conductor 144 by a predetermined distance for insulation purpose therebetween. The insulation between the heat conductive layer 124 and the heater 142 can be achieved using the second passivation layer 122 interposed therebetween. Furthermore, the heat conductive layer 124 contacts the upper surface of the substrate 110 through a second contact hole C₂ formed by penetrating the first and second passivation layers 121 and 122.
The heat conductive layer 124 is made of a metal having good conductivity. When both heat conductive layer 124 and the conductor 144 are formed on the second passivation layer 122, the heat conductive layer 124 may be made of the same material as the conductor 144, such as aluminum, aluminum alloy, gold, or silver.
If the heat conductive layer 124 is formed thicker than the conductor 144 or made of a metal different from that of the conductor 144, an insulating layer (not shown) may be interposed between the conductor 144 and the heat conductive layer 124.
The third passivation layer 126 is provided on the conductor 144 and the second passivation layer 122 for electrical insulation between the overlying metal layer 128 and the underlying conductor 144 and protection of the conductor 144. The third passivation layer 126 may be made of tetraethylorthosilicate (TEOS) oxide or silicon oxide. It is preferable not to form the third passivation layer 126 on an upper surface of the heat conductive layer 124 for contacting the heat conductive layer 124 and the metal layer 128.
The metal layer 128 is made of a high thermal conductive metal such as nickel. Further, the metal layer 128 may be made of copper instead of nickel. The metal layer 128 is formed as thick as about 30-100 µm, preferably, 45 µm or more thick by electrically plating the metal on the third passivation layer 126. To do so, a seed layer 127 for electric plating of the metal is provided on the third passivation layer 126. The seed layer 127 may be made of a metal having good electric conductivity and etching selectivity between the metal layer 128 and the seed layer 127, for example, titanium (Ti) or copper (Cu).
The metal layer 128 functions to dissipate the heat in or around the heater 142 to the outside. Particularly, since the metal layer 128 is relatively thick due to the plating process, effective heat sinking is achieved. That is, the heat residing in or around the heater 142 after ink ejection is transferred to the substrate 110 and the metal layer 128 via the heat conductive layer 124 and then dissipated to the outside. This allows quick heat dissipation after ink ejection and lowers the temperature around the nozzle 138, thereby providing stable printing at a high operating frequency.
As described above, the hydrophobic coating layer 129 is formed on the outer surface of the metal layer 128. Thus, the ink can be ejected in a complete ink droplet form by the hydrophobic coating layer 129 so that the meniscus formed in the nozzle 138 after ink ejection can be stabilized quickly. Further, the hydrophobic coating layer 129 can prevent the surface of the nozzle plate 120 from being polluted by the ink or foreign substance and provide the directionality of the ink ejection. In the present invention, the hydrophobic coating layer 129 is formed only on the outer surface of the metal layer 128 and is not formed on the inner surface of the nozzle 138. That is, the inner surface of the nozzle 138 has a hydrophilic property. Thus, the nozzle 138 can be sufficiently filled with the ink and the meniscus can be maintained in the nozzle 138.
Meanwhile, since the surface of the nozzle plate 120 is continuously exposed to the ink and the air under a high temperature, the nozzle plate 120 corrodes due to ink and oxidizes due to oxygen in the air. The surface of the nozzle plate 120 is wiped periodically so as to remove the residing ink. Thus, the hydrophobic coating layer 129 is required to have an appropriate chemical resistance to oxidization and corrosion and an appropriate abrasion resistance to friction. Therefore, the printhead according to the present invention, the hydrophobic coating layer 129 is made of a material having an appropriate chemical resistance and abrasion resistance as well as a hydrophobic property, for example, at least one of fluorine-containing compound and a metal. Examples of the fluorine-containing compound preferably include polytetrafluoroethylene (PTFE) or fluorocarbon, and examples of the metal preferably include gold (Au).
As described above, the nozzle 138 is formed in the nozzle plate 120. The cross-sectional shape of the nozzle 138 is preferably circular. However, the nozzle 138 may have various cross-sectional shapes such as oval or polygonal ones. The nozzle 138 includes a lower nozzle 138a and an upper nozzle 138b. The lower nozzle 138a is formed by perpendicularly penetrating the first, second, and third passivation layers 121, 122, and 126, and the upper nozzle 138b is formed by perpendicularly penetrating the metal layer 128. While the upper nozzle 138b has a cylindrical shape, it is preferable that the upper nozzle 138b has a tapered shape, in which a cross-sectional area decreases gradually toward an exit, as shown in FIG. 3B. In a case where the upper nozzle 138b has the tapered shape as described above, the meniscus in the ink surface after ink ejection is more quickly stabilized.
Further, as described above, since the metal layer 128 of the nozzle plate 120 is relatively thick, the length of the nozzle 138 can be sufficiently secured. Thus, stable high-speed printing can be provided and the directionality of an ink droplet which is ejected through the nozzle 138 is improved. That is, the ink droplet can be ejected in a direction exactly perpendicular to the substrate 110.
An ink ejection mechanism for an ink-jet printhead according to the present invention will now be described with references to FIGS. 4A through 4C.
Referring to FIG. 4A, if a pulse current is applied to the heater 142 through the conductor 144 when the ink chamber 132 and the nozzle 138 are filled with ink 150, heat is generated by the heater 142. The generated heat is transferred through the first passivation layer 121 underlying the heater 142 to the ink 150 within the ink chamber 132 so that the ink 150 boils to form bubbles 160. As the formed bubbles 160 expand upon a continuous supply of heat, the ink 150 within the nozzle 138 is ejected out of the nozzle 138. At this time, the ink 150 ejected out of the nozzle 138 can be prevented from running on the surface of the nozzle plate 120 by the hydrophobic coating layer 129 formed on the surface of the nozzle plate 120.
Referring to FIG. 4B, if the applied pulse current is interrupted when the bubble 160 expands to its maximum size, the bubble 160 shrinks until it collapses completely. At this time, a negative pressure is formed in the ink chamber 132 so that the ink 150 within the nozzle 138 returns to the ink chamber 132. At the same time, a portion of the ink 150 being pushed out of the nozzle 138 is separated from the ink 150 within the nozzle 138 and ejected in the form of an ink droplet 150' due to an inertial force. At this time, since the hydrophobic coating layer 129 is formed on the surface of the nozzle plate 120 and the sufficient length of the nozzle 138 is secured, the ink droplet 150' can be easily separated from the ink 150 within the nozzle 138 and the directionality of the ink droplet 150' can be improved.
A meniscus in the surface of the ink 150 formed within the nozzle 138 retreats toward the ink chamber 132 after the separation of the ink droplet 150'. At this time, the nozzle 138 is sufficiently long due to the thick nozzle plate 120 so that the meniscus retreats only within the nozzle 138 not into the ink chamber 132. Thus, this prevents air from flowing into the ink chamber 132 and quickly restores the meniscus to its original state, thereby stably maintaining high speed ejection of the ink droplet 150'. Further, since heat residing in or around the heater 142 after the separation of the ink droplet 150' passes through the heat conductive layer 124 and the metal layer 128 and is dissipated into the substrate 110 or to the outside, the temperature in or around the heater 142 and the nozzle 138 drops more quickly.
Next, referring to FIG. 4C, as the negative pressure within the ink chamber 132 disappears, the ink 150 again flows toward the exit of the nozzle 138 due to a surface tension force acting at the meniscus formed in the nozzle 138. The ink 150 is then supplied through the ink channel 134 to refill the ink chamber 132. At this time, since the inner surface of the nozzle 138 have the hydrophilic property, the nozzle 138 can be sufficiently filled with the ink 150. Particularly, when the upper nozzle 138b has the tapered shape, the speed at which the ink 150 flows upward further increases. When the refill of the ink 150 is completed so that the printhead returns to its initial state, the ink ejection mechanism is repeated. During the above process, the printhead can thermally recover its original state more quickly because of heat dissipation through the heat conductive layer 124 and the metal layer 128.
A method for manufacturing a monolithic ink-jet printhead as presented above according to a preferred embodiment of the present invention will now be described.
FIGS. 5 through 16 are cross-sectional views for explaining a method for manufacturing the monolithic ink-jet printhead having the nozzle plate according to a preferred embodiment of the present invention.
Referring to FIG. 5, a silicon wafer used for the substrate 110 has been processed to have a thickness of approximately 300-500 µm. The silicon wafer is widely used for manufacturing semiconductor devices and is effective for mass production.
While FIG. 5 shows a very small portion of the silicon wafer, the ink-jet printhead according to the present invention can be manufactured in tens to hundreds of chips on a single wafer.
The first passivation layer 121 is formed on an upper surface of the prepared silicon substrate 110. The first passivation layer 121 may be formed by depositing silicon oxide or silicon nitride on the upper surface of the substrate 110.
Next, the heater 142 is then formed on the first passivation layer 121 on the upper surface of the substrate 110. The heater 142 may be formed by depositing a resistive heating material, such as polysilicon doped with impurities, tantalum-aluminum alloy, tantalum nitride, titanium nitride, or tungsten silicide, on the entire surface of the first passivation layer 121 to a predetermined thickness and then patterning it. Specifically, the polysilicon doped with impurities such as a phosphorus (P)-containing source gas may be deposited by low pressure chemical vapor deposition (LPCVD) to a thickness of about 0.7-1 µm. Tantalum-aluminum alloy, tantalum nitride, titanium nitride, or tungsten silicide may be deposited by sputtering to a thickness of about 0.1-0.3 µm. The deposition thickness of the resistive heating material may be determined in a range other than given here to have an appropriate resistance considering the width and length of the heater 142. The resistive heating material deposited on the entire surface of the first passivation layer 121 can be patterned by a photo process using a photomask and a photoresist and an etching process using a photoresist pattern as an etch mask.
Then, as shown in FIG. 6, the second passivation layer 122 is formed on the first passivation layer 121 and the heater 142 by depositing silicon oxide or silicon nitride to a thickness of about 0.5-3 µm. The second passivation layer 122 is then partially etched to form the first contact hole C₁ exposing a portion of the heater 142 to be connected with the conductor 144 in a step shown in FIG. 7. The second and first passivation layers 122 and 121 are sequentially etched to form the second contact hole C₂ exposing a portion of the substrate 110 to contact the heat conductive layer 124 in the step shown in FIG. 7. The first and second contact holes C₁ and C₂ can be formed simultaneously.
FIG. 7 shows the state in which the conductor 144 and the heat conductive layer 124 have been formed on the upper surface of the second passivation layer 122. Specifically, the conductor 144 and the heat conductive layer 124 can be formed at the same time by depositing a metal having excellent electric and thermal conductivity such as aluminum, aluminum alloy, gold or silver using a sputtering method to a thickness of about 1 µm and then patterning it. At this time, the conductor 144 and the heat conductive layer 124 are formed to insulate from each other, so that the conductor 144 is connected to the heater 142 through the first contact hole C₁ and the heat conductive layer 124 contacts the substrate 110 through the second contact hole C₂.
Meanwhile, if the heat conductive layer 124 is to be formed thicker than the conductor 144 or if the heat conductive layer 124 is to be made of a metal different from that of the conductor 144, or if further ensure insulation between the conductor 144 and the heat conductive layer 124 is achieved, the heat conductive layer 124 can be formed after forming the conductor 144. More specifically, in the step shown in FIG. 6, after forming only the first contact hole C₁, the conductor 144 is formed. An insulating layer (not shown) is then formed on the conductor 144 and the second passivation layer 122. The insulating layer can be formed from the same material using the same method as the second passivation layer 122. The insulating layer and the second and first passivation layers 122 and 121 are then sequentially etched to form the second contact hole C₂. Further, the heat conductive layer 124 is formed using the same method as the second passivation layer 122. Thus, the insulating layer is interposed between the conductor 144 and the heat conductive layer 124.
FIG. 8 shows the state in which the third passivation layer 126 has been formed on the entire surface of the resultant structure of FIG. 7. Specifically, the third passivation layer 126 may be formed by depositing tetraethylorthosilicate (TEOS) oxide using plasma enhanced chemical vapor deposition (PECVD) to a thickness of approximately 0.7-3 µm. Then, the third passivation layer 126 is partially etched to expose the heat conductive layer 124.
FIG. 9 shows the state in which the lower nozzle 138a has been formed. The lower nozzle 138a is formed by sequentially etching the third, second, and first passivation layers 126, 122, and 121 on the inside of the heater 142 using reactive ion etching (RIE).
FIG. 10 shows the state in which a seed layer 127 for electric plating has been formed on the entire surface of the resultant structure of FIG. 9. To carry out electric plating, the seed layer 127 can be formed by depositing metal having good conductivity such as titanium (Ti) or copper (Cu) to a thickness of approximately 100-1,000 Å using sputtering method. The metal consisting of the seed layer 127 is determined in consideration of the etching selectivity between the metal layer 128 and the seed layer 127 as described latter. Meanwhile, the seed layer 127 may be formed in a composite layer by sequentially stacking nickel (Ni) and copper (Cu).
Next, as shown in FIG. 11, a plating mold 139 for forming the upper nozzle 138b (refer to FIG. 14) is prepared. The plating mold 139 can be formed by applying photoresist on the entire surface of the seed layer 127 to a predetermined thickness, and then patterning it in the same shape as that of the upper nozzle 138b. Meanwhile, the plating mold 139 may be made of photosensitive polymer. Specifically, the photoresist is first applied on the entire surface of the seed layer 127 to a thickness slightly higher than the height of the upper nozzle 138b. At this time, the photoresist is filled in the lower nozzle 138a. Next, the photoresist is patterned to remain only the photoresist filled in a portion where the upper nozzle 138b will be formed and the photoresist filled in the lower nozzle 138a. At this time, the photoresist is patterned in a tapered shape in which a cross-sectional area gradually increases downward. The patterning process can be performed by a proximity exposure process for exposing the photoresist using a photomask which is separated from an upper surface of the photoresist by a predetermined distance. In this case, light passed through the photomask is diffracted so that a boundary surface between an exposed area and a non-exposed area of the photoresist is inclined. An inclination of the boundary surface and the exposure depth can be adjusted by a space between the photomask and the photoresist and an exposure energy in the proximity exposure process. Meanwhile, the upper nozzle 138b may be formed in a cylindrical shape, and in this case, photoresist is patterned in a pillar shape.
Next, as shown in FIG. 12, the metal layer 128 is formed to a predetermined thickness on the upper surface of the seed layer 127. The metal layer 128 can be formed to a thickness of about 30-100 µm, preferably, 45 µm or more by electrically plating nickel (Ni) or copper (Cu), preferably, nickel (Ni) on the surface of the seed layer 127. Specifically, the plating process using nickel (Ni) can be performed using a nickel sulfamate solution. At this time, the plating process using nickel (Ni) is completed just before a top portion of the plating mold 139 is plated.
Next, as shown in FIG. 13, the hydrophobic coating 129 is formed on the surface of the metal layer 128. The coating layer 129, as described above, may be made of a material having the chemical resistance and the abrasion resistance as well as the hydrophobic property, for example, at least one of fluorine-containing compound and metal. Examples of the fluorine-containing compound preferably include PTFE or fluorocarbon, and examples of the metal preferably include gold (Au). The PTFE, fluorocarbon, and gold can be coated on the surface of the metal layer 128 to a predetermined thickness by proper methods, respectively. For example, in a case of using PTFE, a metaflon process for compositely plating PTFE and nickel (Ni) on the surface of the metal layer 128 to a thickness of about 0.1 µm to several µm can be employed. Meanwhile, in a case of using fluorocarbon, fluorocarbon can be deposited on the surface of the metal layer 128 using the PECVD to a thickness of several Å to hundreds Å. At this time, fluorocarbon is deposited on the plating mold 139 and then the fluorocarbon deposited on the plating mold 139 can be removed together with the plating mold 139 in a process of removing the plating mold 139 which will be described below. In a case using of gold, gold can be formed on the surface of the metal layer 128 using an evaporator to a thickness of 0.1-1 µm.
As described above, in the present invention, since the metal layer 128 and the hydrophobic coating 129 are formed after forming the plating mold 139 in a portion where the nozzle 138 will be formed, the hydrophobic coating 129 is formed only on the outer surface of the metal layer 128 and is not formed inside the nozzle 138.
Next, the plating mold 139 is removed, and then a portion of the seed layer 127 exposed by the removal of the plating mold 139 is removed. The plating mold 139 can be removed using a general photoresist removal method, for example, acetone. The seed layer 127 can be wet-etched using an etching solution, in which only the seed layer 127 can be selectively etched considering the etching selectivity between a material consisting of the metal layer 128 and a material consisting of the seed layer 127. For example, when the seed layer 127 is made of copper (Cu), an acetate base solution can be used as an etching solution, and when the seed layer 127 is made of titanium (Ti), an HF base solution can be used as an etching solution. As a result, as shown in FIG. 14, the lower nozzle 138a and the upper nozzle 138b are connected to each other so that the complete nozzle 138 is formed and the nozzle plate 120 formed by stacking the plurality of material layers is completed.
FIG. 15 shows the state in which the ink chamber 132 of a predetermined depth has been formed on the upper surface of the substrate 110. The ink chamber 132 can be formed by isotropically etching the substrate 110 exposed by the nozzle 138. Specifically, dry etching is carried out on the substrate 110 using XeF₂ gas or BrF₃ gas as an etch gas for a predetermined time to form the hemispherical ink chamber 132 with a depth and a radius of about 20-40 µm as shown in FIG. 15.
FIG. 16 shows the state in which the manifold 136 and the ink channel 134 have been formed by etching the substrate 110 from its rear surface. Specifically, an etch mask that limits a region to be etched is formed on the rear surface of the substrate 110, and wet etching on the rear surface of the substrate 110 is then performed using tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH) as an etching solution to form the manifold 136 with an inclined side surface. Alternatively, the manifold 136 may be formed by anisotropically dry-etching the rear surface of the substrate 110. Subsequently, an etch mask that defines the ink channel 134 is formed on the rear surface of the substrate 110 where the manifold 136 has been formed, and the substrate 110 between the manifold 136 and the ink chamber 132 is then dry-etched by RIE, thereby forming the ink channel 134. Meanwhile, the ink channel 134 may be formed by etching the substrate 110 at the bottom of the ink chamber 132 through the nozzle 138.
After having undergone the above steps, the monolithic ink-jet printhead according to the present invention having the structure as shown in FIG. 16 is completed.
As described above, a monolithic ink-jet printhead and a method for manufacturing the same according to the present invention have the following advantages.
First, since a metal layer and a hydrophobic coating layer are formed after forming a plating mold in a portion where a nozzle will be formed, the hydrophobic coating layer is formed only on an outer surface of the metal layer and the nozzle has the hydrophobic property. Thus, ink ejection factors such as a directionality, a size, and an ejection speed of an ink droplet are improved so that an operating frequency can increase and a printing quality can be improved. Further, a surface of the printhead can be prevented from being polluted and have improved chemical resistance and abrasion resistance.
Second, the thick metal layer can be formed by electric plating so that a heat sinking capability is increased, thereby increasing the ink ejection performance and an operating frequency. Further, a sufficient length of the nozzle can be secured according to the thickness of the metal layer so that a meniscus can be maintained within the nozzle, stable ink refill operation is allowed, and the directionality of the ink droplet to be ejected is improved.
Third, since a nozzle plate having a nozzle is formed integrally with a substrate having an ink chamber and an ink channel formed thereon, an ink-jet printhead can be manufactured on a single wafer using a single process. This eliminates the conventional problem of misalignment between the ink chamber and the nozzle.
While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims. For example, materials used to form the constitutive elements of a printhead according to the present invention may not be limited to those described herein. In addition, the stacking and formation method for each material are only examples, and a variety of deposition and etching techniques may be adopted. Furthermore, specific numeric values illustrated in each step may vary within a range in which the manufactured printhead can operate normally. Also, sequence of process steps in a method of manufacturing the printhead according to the present invention may differ.

Claims

A monolithic ink-jet printhead comprising:
a substrate (110) which has an ink chamber (132) filled with ink to be ejected, a manifold (136) for supplying ink to the ink chamber, and an ink channel (134) for connecting the ink chamber with the manifold;

a nozzle plate (120) which includes a plurality of passivation layers (121, 122, 126) sequentially stacked on the substrate, a metal layer (128) formed on the plurality of passivation layers, and a nozzle (138), through which ink is ejected from the ink chamber by penetrating the nozzle plate;

a heater (142) which is provided between the passivation layers and located above the ink chamber for heating ink within the ink chamber;

a conductor (144) which is provided between the passivation layers and is electrically connected to the heater for applying a current to the heater; and

a hydrophobic coating layer (129) which is formed only on an outer surface of the metal layer.
The printhead of claim 1, wherein the hydrophobic coating layer is made of at least one of a fluorine-containing compound and a metal.
The printhead of claim 2, wherein the hydrophobic coating layer includes a fluorine-containing compound which includes polytetrafluoroethylene (PTFE) or fluorocarbon.
The printhead of claim 2 or 3, wherein the hydrophobic coating layer includes a metal which includes gold (Au).
The printhead of any one of claims 1 to 4, wherein the metal layer is made of nickel (Ni).
The printhead of any one of claims 1 to 5, wherein the metal layer is formed by electric plating to a thickness of 30-100 µm.
The printhead of any one of claims 1 to 6, wherein the nozzle includes a lower nozzle formed on the plurality of passivation layers and an upper nozzle formed on the metal layer.
The printhead of claim 7, wherein the upper nozzle has a tapered shape in which a cross-sectional area decreases gradually toward an exit.
The printhead of any one of claims 1 to 8, wherein the nozzle plate further includes a heat conductive layer (124) which is located above the ink chamber and insulated from the heater and the conductor, and which thermally contacts the substrate and the metal layer.
The printhead of claim 9, wherein the heat conductive layer is made of any one of aluminum, aluminum alloy, gold, or silver.
A method for manufacturing a monolithic ink-jet printhead, the method comprising:
(a) preparing a substrate (110);

(b) forming a heater (142) and a conductor (144) connected to the heater between a plurality of passivation layers (121, 122, 126) while sequentially stacking the plurality of passivation layers on the substrate;

(c) forming a lower nozzle by etching the passivation layers to penetrate the passivation layers;

(d) forming a metal (128) layer on the passivation layers, forming a hydrophobic coating layer (129) on an outer surface of the metal layer, and forming an upper nozzle connected to the lower nozzle by penetrating the metal layer and the hydrophobic coating layer;

(e) etching an upper surface of the substrate exposed through the upper nozzle and the lower nozzle to form an ink chamber (132); and

(f) etching the substrate to form a manifold (136) for supplying ink and an ink channel for connecting the ink chamber with the manifold.
The method of claim 11, wherein in (a), the substrate is made of a silicon wafer.
The method of claim 11 or 12, wherein in (b), a heat conductive layer (124) which is located above the ink chamber, insulated from the heater and the conductor, and thermally contacts the substrate and the metal layer is formed between the passivation layers.
The method of claim 13, wherein the heat conductive layer and the conductor are simultaneously formed from the same metal.
The method of claim 13 or 14, wherein after forming an insulating layer on the conductor, the heat conductive layer is formed on the insulating layer.
The method of any one of claims 13 to 15, wherein the heat conductive layer is made of any one of aluminum, aluminum alloy, gold, or silver.
The method of any one of claims 11 to 16, wherein in (c), the lower nozzle is formed by dry etching the passivation layers on the inside of the heater using reactive ion etching (RIE).
The method of any one of claims 11 to 17, wherein (d) includes:
forming a seed layer for electric plating on the passivation layers;

forming a plating mold for forming the upper nozzle on the seed layer;

forming the metal layer on the seed layer by electric plating;

forming the hydrophobic coating layer only on the outer surface of the metal layer; and

removing the plating mold and the seed layer formed under the plating mold.
The method of claim 18, wherein the seed layer is formed by depositing at least one of titanium and copper on the passivation layers.
The method of claim 19, wherein the seed layer includes a plurality of metal layers formed by sequentially stacking titanium and copper.
The method of any one of claims 18 to 20, wherein the plating mold is formed by depositing photoresist or photosensitive polymer on the seed layer to a predetermined thickness and then patterning it in the same shape as that of the upper nozzle.
The method of claims 21, wherein the plating mold is formed by patterning the photoresist or the photosensitive polymer in a tapered shape, in which a cross-sectional area gradually increases downward, by a proximity exposure for exposing the photoresist or the photosensitive polymer using a photomask which is installed to be separated from a surface of the photoresist or the photosensitive polymer by a predetermined distance.
The method of claim 22, wherein an inclination of the plating mold is adjusted by a space between the photomask and the photoresist or the photosensitive polymer and an exposure energy.
The method of any one of claims 18 to 23, wherein the metal layer is made of nickel.
The method of any one claims 18 to 24 wherein the metal layer is formed to a thickness of 30-100 µm.
The method of any one of claims 18 to 25, wherein the hydrophobic coating layer is made of at least one of a fluorine-containing compound and a metal.
The method of claim 26, wherein the hydrophobic coating layer includes a fluorine-containing compound which includes polytetrafluoroethylene (PTFE) or fluorocarbon.
The method of claim 27, wherein the fluorine-containing compound includes PTFE, and the PTFE and nickel are compositely plated on the surface of the metal layer.
The method of claim 27, wherein the fluorine-containing compound includes fluorocarbon which is deposited on the surface of the metal layer using the PECVD.
The method of any of claims 26 to 29, wherein the hydrophobic coating layer includes a metal which includes gold (Au).
The method of claim 30, wherein gold is deposited on the surface of the metal layer using an evaporator.
The method of any one of claims 11 to 31, wherein in (e), the substrate exposed through the nozzle is dry etched isotropically to form the ink chamber.
The method of any one of claims 11 to 32, wherein in (f), the lower surface of the substrate is etched to form the manifold, and the substrate is etched to penetrate the substrate between the manifold and the ink chamber to from the ink channel.